Surgical visual feedback and eye fixation method and apparatus

ABSTRACT

A fixation apparatus is provided that limits rotation of the ocular globe of an eye, to facilitate alignment of an instrument with the axis of astigmatism of the eye. The apparatus includes fixation target means ( 12 ) for locating in the field of view of the eye so that the eye may fixate on the target. The fixation target means includes or consists of at least one elongate component ( 16 ). Also disclosed is a corresponding method, and method and apparatus for supplying visual feedback to an operator during refractive surgery of an eye of a patient.

FIELD OF THE INVENTION

The present invention relates, in different aspects, to eye fixation andto the provision of visual feedback to a surgeon, during the delivery ofmedical laser procedures, particularly in the fields of ophthalmicsurgical procedures, such as Photorefractive Keratectomy (PRK) andLaser-in-situ Keratomileusis (LASIK), or any laser based refractivecorrection. The invention will be described with reference to theseapplications, though it is to be understood that other applications areenvisaged.

BACKGROUND ART

Most existing refractive laser delivery systems provide little feedbackfor the operator (typically a surgeon). Usually a crosshair graticule issuperimposed through the microscope optics to help the operator aim thelaser beam correctly onto the cornea. A fixation target or light, suchas a flashing LED, is used to ensure that the patient's eye remainscorrectly aligned during the surgery. However, this arrangement does notnecessarily provide the best alignment of the eye and the laser beam,nor does it provide visual feedback for the operator concerning thestatus of the eye or the laser. It may at times be necessary for theoperator to move his or her attention away from the surgical field tocheck on instrumentation, such as the microkeratome or the laser source.The axis of astigmatism of the patient's eye is also likely to bemisaligned when the patent is supine and fixating on a point of light.

Refractive errors are usually assessed when the patient is seated in anupright position using structured shapes or symbols, such as letters ofthe alphabet. However, refractive surgery is usually performed with thepatient reclining in an operating chair. It has been found that, when apatient lies recumbent, the ocular globe is liable to rotate, alteringthe position of the axis of astigmatism between 7° and 16° in 25% ofcases (Smith, Talamo, Assil & Petashnick, “Comparison of Astigmatic Axisin the Seated and Supine Positions”, J. of Refractive & Corneal Surgery10(6), 615 (1994)). This occurs for two reasons: i) the removal of thereference horizon, and ii) the change from binocular to monocularvision. Focussing on a point of light (the flashing LED), instead of thelinear horizon, does not provide a proper point of horizontal orvertical reference. The globe is therefore liable to rotatefractionally, possibly resulting in misalignment of the treatment of theeye's axis of astigmatism. The potential end result is under-treatmentof the original astigmatic error or inducement of astigmatism at anotheraxis.

U.S. Pat. No. 5,549,597 describes a method for determining the axis ofastigmatism of a patient undergoing refractive surgery, so as to providereal-time alignment information for the surgical procedure. The patientis required to focus on a target such as three sets of three lines ofvariable line spacing, each set corresponding to a different visualacuity, and then to focus on the best resolved set of lines and rotatethe target until the finest line is seen most clearly. This method ofdetermining the axis of astigmatism and aligning the surgical laser isnot ideal. The patient is forced to make subjective comparisons at ahighly stressful time. In addition, the globe may still rotate after thealignment has been performed, and prior to surgery.

An earlier configuration for determining the axis of astigmatism isdescribed in U.S. Pat. No. 3,785,723, and involves rotation of an opaquedisk having multiple small apertures backlit by a light source so as toresemble a set of point light sources arranged in a straight line alongthe diameter of the disk.

U.S. Pat. No. 5,442,412 discloses a patient responsive eye fixationtarget for use in ophthalmic procedures in which respective lightsources produce a ring of light and a dot of light centred on the sameoptical axis, but respectively closer to and further from the eye. Inresponse to detection of a quantifiable amount of eye movement, the dotis altered in appearance, eg. by flashing or colour changes, to alertthe patient that his or her eye is no longer aligned with the dot andring.

Corresponding to the patient fixation apparatus is the apparatus used bythe surgeon to view and assess the extent of fixation and the alignmentof the laser beam. The surgeon views this display when looking down thesurgical microscope. Current technology provides a display including agraticule or crosshair. A He-Ne beam is sometimes provided for aimingthe surgical beam.

U.S. Pat. No. 4,870,964 provides a head-up display for use with anoperating microscope during phaco-emulsification procedures. Thisapparatus allows the operating surgeon to view information about thestatus of the patient, the eye and operating equipment, such as vacuumpressure, without removing their gaze from the operating field. It doesso by projecting light onto the operating field of the eye andconditioning the reflections from the cornea so that interpretableimages may be viewed by the surgeon as they look down the microscope.U.S. Pat. No. 5,135,299 describes a similar operating microscopefeaturing a head-up display, produced by reflecting operationalinformation from the scleral portion of the eye.

It is an object of the present invention, in at least one aspect, toprovide an eye fixation method and apparatus that is simple andreliable, and involves minimal expectation of the patient. Forparticular applications, it is further preferred that the arrangementreduces the angular rotation of the ocular globe to facilitate alignmentof an instrument with the axis of astigmatism.

It is an object of another aspect of the present invention to provide asurgical visual feedback method and apparatus that provides increasedinformation to the surgeon or operator.

SUMMARY OF THE INVENTION

According, therefore, to a first aspect of the present invention, thereis provided a method for limiting the rotation of the ocular globe of aneye to facilitate alignment of an instrument with the axis ofastigmatism of the eye. The method includes providing fixation targetmeans in the field of view of the eye so that the eye may fixate on thetarget. The fixation target means includes or consists of at least oneelongate component having a fixed orientation.

Preferably the method includes providing the fixation target means byway of light emitting means. Preferably, the light emitting means isstrobed.

The present invention also provides, in its first aspect, a fixationapparatus that limits rotation of the ocular globe of an eye, tofacilitate alignment of an instrument with the axis of astigmatism ofthe eye. The apparatus includes fixation target means for locating inthe field of view of the eye so that the eye may fixate on the target.The fixation target means includes or consists of at least one elongatecomponent having a fixed orientation.

Preferably, said fixation target means includes or consists of at leasttwo intersecting substantially mutually perpendicular elongatecomponents. The fixation target means may consist substantially of across, and/or it may include more than two elongate components arrangedas a grid. The fixation target means preferably has a fixed orientation.

The fixation target means may be a light emitting means. Moreover, theor each elongate component may be defined by the light emitting means.

Preferably, the light emitting means includes a plurality of lightemitting diodes (LEDs) arranged in a respective linear array to definethe or each elongate component.

Preferably the apparatus includes a printed circuit board (PCB) on whichthe LEDs are mounted.

Preferably the apparatus is controllable to strobe the light emittingmeans.

The apparatus may include a pulsable power supply to strobe the lightemitting means.

In its first aspect, the invention extends to laser surgery apparatusincorporating patient observable fixation apparatus as described above.

In a second aspect of the present invention there is provided a methodfor supplying visual feedback to an operator during refractive surgeryof an eye of a patient, including:

-   -   1) providing fixation target means for the eye to fixate upon;    -   2) locating the eye for viewing by viewing means while it is        fixated upon said fixation target means;    -   3) generating an information display of information pertinent to        said surgery and suitable for displaying visually; and    -   4) transmitting the information display to the viewing means for        viewing by the operator;    -   whereby the eye and the information display may be viewed        simultaneously by the operator.

Preferably the method includes updating the information display.

Preferably step 3) includes generating the information display with acontroller means.

Preferably the controller means is a computer.

Preferably the method includes transmitting the information display to adisplay means and displaying the information display on the displaymeans.

The display means may be miniature TV or LCD screen or a plurality ofLEDs.

Preferably step 1) includes the alignment facilitating method accordingto the first aspect of the invention.

Preferably the viewing means includes left and right optics means, andthe target is located between the left and right optics means.

Preferably the viewing means is a surgical microscope.

The invention extends to a method of performing refractive surgery on aneye of a patient, wherein visual feedback is supplied in accordance withthe method of the second aspect of the invention. The refractive surgerymay eg. be PRK or LASIK, thermal keratoplasty, intrastromal ablation orany other surgical method that alters the refraction of the eye.

The method may be performed with any laser suitable for use in surgerythat involves altering the refractive properties of the eye, e.g. anultraviolet ablation laser, a Holmium laser, or an Erbium laser at 3microns.

Preferably step 4) includes viewing said information by means of a beamsplitter or plate of glass.

In its second aspect, the invention also provides an apparatus forsupplying visual feedback to an operator during refractive surgery of aneye. The apparatus includes fixation target means for the eye to fixateupon, and viewing means for viewing the eye while it is fixated upon thefixation target means. Controller means is provided for generating aninformation display, and screen means displays the said informationdisplay, for viewing by the viewing means, whereby the eye and theinformation display may be viewed simultaneously by the operator.

Preferably the apparatus includes display means for displaying theinformation display.

The apparatus may be provided in combination with a surgical laser andthereby comprise laser surgery apparatus.

The laser may be any laser suitable for use in surgery that involvesaltering the refractive properties of the eye, such as a ultravioletablation laser, a Holmium laser, an Erbium laser at 3 microns or anyother appropriate laser source.

Preferably the target means is a fixation apparatus according to thefirst aspect of the invention.

The display means and/or screen means may be viewed by means of a beamsplitter or plate of glass.

Preferably the display means is a miniature TV or LCD screen or aplurality of LEDs.

Preferably the viewing means is a surgical microscope.

Preferably the controller means is a computer.

Preferably the viewing means includes left and right optics, and thetarget is located between the left and right optics.

In the method and apparatus of the second aspect of the invention, theinformation may include an alert signal indicating misalignment of thepatient's eye, eg. due to straying from fixation upon the fixationtarget means.

The information may pertain to one or more of: the status of thepatient, the surgery or the equipment, the position of the eye or wherean eye-tracker is aiming the laser.

The information may include one or more of the following elements ofoperational information: type of treatment, number of laser pulsesrequired to finish, operation time remaining, patient identification andwhich eye is being treated, keratometry information, refractioninformation, and/or topographical information.

The information may include microkeratome status information, such assuction and blade speed readings.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention be more fully understood, preferredembodiments will now be described, by way of example, with reference tothe accompanying drawings, in which:

FIG. 1 is a schematic view of an eye fixation apparatus according to apreferred embodiment of the first aspect of the present invention;

FIG. 2 is a fragmentary view illustrating a suitable location for theeye fixation target; and

FIG. 3 is a diagram of the layout of the principal components of anarrangement for supplying visual feedback to an ophthalmic surgeonduring refractive laser eye surgery procedures, according to a preferredembodiment of the second aspect of the present invention, but preferablyincorporating the embodiment of FIGS. 1 and 2.

PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2, there is presented a schematic view of apatient's eye fixation apparatus 10 according to a preferred embodimentof the present invention. The apparatus 10 includes a fixation target inthe form of a cross 12 formed by surface mounted light emitting diodes,LEDs 14, arranged in two linear arrays to define intersecting elongatecomponents or axes 16, 18 perpendicular to one another. The LEDs arefixed to a printed circuit board (PCB) 13, in turn arranged on anelongate lipped substrate 15. Substrate 15 is positioned on the front ofthe surgical microscope 28, symmetrically between the adjacent stereooculars 40,42, so as to be clearly observable by the patient.Alternatively, cross 12 may be located elsewhere within the surgicallaser, and projected to optically appear as if it is placed between theoculars of the microscope.

Substrate 15 is fixed in position on the microscope so that cross 12 hasa fixed orientation. “Vertical” axis 16 of the cross 12 of LEDs 14 islonger than “horizontal” axis 18, by providing several more LEDs 14 inaxis 16 than axis 18. By “vertical” is meant the axis that extendsnormal to the lines joining the oculars. The LEDs 14 may alternativelybe positioned to form any other pattern of elongate or linear elements,such as a line or a grid.

The cruciform arrangement of LEDs 14 allows the patient to better judgehorizontal and vertical directions, so that the ocular globe(s) of thepatient does not rotate and the axis of astigmatism is naturallyaligned.

A suitable control circuit 20, of a simple form readily apparent tothose skilled in the art, is provided for strobing LEDs 14 in apre-selected, perhaps adjustable, sequence. The LEDs may, for example,flash in unison or in a more complex pattern. LEDs 14 may be of varyingcolours to facilitate patient concentration and gaze control. In use,the patient is required to fixate his or her gaze on the flashing cross12, thereby preventing angular rotation of the ocular globe andmisalignment of the treatment eye's axis of astigmatism. A preferredflash rate is about 1.5 Hz with a duty cycle of about 50%. The dutycycle may be adjustable, for example to allow more light during LASIKand less light during PRK.

FIG. 3 is a diagram of an apparatus 22 for supplying visual feedback toan ophthalmic surgeon during refractive laser eye surgery proceduresbeing performed on an eye 24. This apparatus is an embodiment of thesecond aspect of the invention. The apparatus 22 includes a surgicalmicroscope 28′, a fixation target 26, which is preferably a flashingcross 12′ as in FIGS. 1 and 2, on microscope 28′, a head-up display 30to give the surgeon feedback regarding patient fixation, the operatingconditions and other pertinent information, and an imaging device in theform of a miniaturised TV or LCD screen 32 supplied within the laserdelivery head (not shown). The head-up display 30 may be produced byprojecting lights onto a surface, as is known in the art, and may bedisplayed on screen 32. The imaging device may alternatively comprise acombination of light emitting diodes.

The apparatus 22 further includes a controller in the form of computer34 and; communications link 36 between computer 34 and screen 32.Computer 34 generates the information content (comprising informationpertinent to the operation being carried out) of the head-up display 30,and transmits this content via link 36 to screen 32 to display. Thiscontent could include a pulse countdown, operation time remaining, analert signal indicating misalignment of the patient's eye, a cross 31indicating where the laser is currently aimed, patient information suchas name or ID, treatment zone information, topographical information andany other information that the surgeon may deem useful.

The apparatus 22 also includes a beamsplitter 38, by which the head-updisplay 30 is viewed. The beamsplitter 38 forms a part of the optics ofthe laser (not shown), for relaying this information towards oculars40′, 42′ of the microscope 28′, so that the operator may see theinformation when he or she looks down the microscope 28′.

Thus, in use, while the patient views (50) a suitable fixation target 26(such as a fixation cross 12′ as described above), the surgeon is ableto view the patient's eye 24 (51) and the head-up display 30 (52)through the surgical microscope 28′.

1. In refractive laser surgery apparatus, a fixation apparatus forlimiting rotation of an ocular globe of an eye of a patient duringrefractive laser surgery on the eye, to facilitate alignment of thesurgery apparatus with an axis of astigmatism of the eye, comprising:fixation target means disposed at a patient observable position in afield of view of said eye so that said eye may fixate on said target;wherein said target means comprises light emitting means that whenactivated defines at least two intersecting, substantially mutuallyperpendicular elongate components, each having a location andorientation that remains fixed during said surgery on the eye, therebylimiting rotation of the ocular globe of the patient's eye during saidsurgery.
 2. Apparatus according to claim 1 wherein said fixation targetmeans includes at least two intersecting components.
 3. Apparatusaccording to claim 1 wherein said fixation target means consistssubstantially of a cross.
 4. Apparatus according to claim 1 wherein oneof the at least two elongate components is longer than the other. 5.Apparatus according to claim 1 wherein said fixation target meansincludes more than two elongate components arranged as a grid. 6.Apparatus according to claim 1 wherein said fixation target means is alight emitting means.
 7. Apparatus according to claim 6 wherein the oreach said elongate component is defined by said light emitting means. 8.Apparatus according to claim 6, further including means to strobe saidlight emitting means.
 9. Apparatus according to claim 1, wherein saidlight emitting means includes a plurality of light emitting diodesarranged in a respective linear array to define the or each saidelongate component.
 10. Apparatus according to claim 9, furtherincluding a printed circuit board (PCB) on which the light emittingdiodes are mounted.
 11. Laser surgery apparatus incorporating patientobservable fixation apparatus according to claim
 1. 12. Laser surgeryapparatus according to claim 1, wherein said fixation target means isdisposed in a patient observable position on a surgical microscope ofsaid laser surgery apparatus.
 13. Laser surgery apparatus according toclaim 12 wherein said at least one elongate component is arranged in a“vertical” orientation on said surgical microscope.
 14. An apparatusaccording to claim 1, wherein said fixation target means has a fixedorientation.
 15. In refractive laser surgery on an eye of a patient, amethod for limiting rotation of an ocular globe of said eye during saidsurgery, to facilitate alignment of surgery apparatus with an axis ofastigmatism of the eye, comprising providing fixation target means at apatient observable position in the field of view of said eye so thatsaid eye may fixate on said target, wherein said fixation target meanscomprises activated light emitting means that defines at least twointersecting substantially mutually perpendicular elongate componentseach having a location and orientation that remains fixed during saidsurgery on the eye, thereby limiting rotation of the ocular globe of thepatient's eye during said surgery.
 16. A method according to claim 15,wherein said fixation target means includes or consists of at least twointersecting, substantially mutually perpendicular elongate components.17. A method according to claim 15, wherein said fixation target meansconsists substantially of a cross.
 18. A method according to claim 15,wherein said fixation target means includes more than two componentsarranged as a grid.
 19. A method according to claim 15, includingproviding said fixation target means by way of light emitting means. 20.A method according to claim 15, wherein said light emitting meansincludes a plurality of light emitting diodes arranged in a respectivelinear array to define the or each said elongate component.
 21. A methodaccording to claim 15, further including strobing of said light emittingmeans.
 22. A method according to claim 15, wherein said fixation targetmeans is provided so as to have a fixed orientation.